Continuous Crack Monitoring of Metallic Structures Using Carbon Nanotube-based Epoxy Thin Films

摘要

This work focuses on the application of epoxy nanocomposite thin film sensors forrncontinuous monitoring of crack evolution in metallic structures. The approach takenrnwas to monitor the current or resistance change in these nanocomposite films as cracksrndeveloped and propagated in the metallic host structure. Based on optical, electricalrnand mechanical properties of epoxy resins modified with different contents of singlewalledrncarbon nanotubes (SWCNT), two different nanocomposites (with 0.3 wt% andrn1.0 wt% of SWCNT) were chosen for the development of a crack sensor. Thernperformance of the nanocomposite sensors was evaluated under tension-tensionrnfatigue tests on aluminum coupons with centrally located through thickness electricalrndischarge machined (EDM) notches. Crack growth in the aluminum was found torntransfer to the nanocomposite films in a stable mode. Once the crack was established,rna linear correlation was found between the measured current and crack length with arnslope of -10~(-11) A/mm and -10~(-8) A/mm for nanocomposites, with 0.3 wt% and 1.0 wt%rnof SWCNT, respectively. Contact between the asperities formed on the crack surfacesrnin the nanocomposite film while the crack was closed was found to be an importantrnlimiting factor causing a large variation in measured currents during each fatiguerncycle. In summary, the nanocomposite thin film sensor developed in this work offersrncontinuous crack growth monitoring. The sensor is also suitable for visual inspectionrnof the host structure due to the transparency of the developed nanocomposite film.